Brake test

Me Too

I'd be interested in watching/helping/playing

Paul
 
Tim we can come to you if you like. If not I would be willing to host as I have lots of room if others would like to join. I need to be done by 3pm for an evening function.
 
Mike, if you have room, that would be great. I'll look up your address on the members list. See you at your place at 9am! :D
 
Sounds good. I have level driveway for at least 4 cars for working and unlimited parking on grass and private street. I also have 2 floor jacks, 2 jack stands, and most tools we could need. If you need a special tool to remove your caliper then bring it. I have 2 impact guns if needed. Of course Tim bring the caliper tester.


Looking forward to getting some data.
 
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Mike, up to you, but best to take your personal info down off the public area of the site. Best to PM that info. There is a 70% chance it won't rain, but, in case it does, we will re-schedule.
 
Good point Tim, done. I sent info to Tim, Keith, and Paul. Anybody else interested check in and I will send out my info.

All are welcome.
 
So in case it rains, I will be there anyway with the tool in my truck.
 
Rain here in St charles, headed up to Mike's in the truck. Anyone else coming?
 
Tim and Keith came over today with the brake caliper pressure guages. They are pretty slick. What we found was pretty sad.

1. The proportioning valve I installed in the front circuit has broken already and is doing nothing.

2. I have a bad rear caliper. The clamping force of the right caliper was nearly half that of the left. So when both fronts were providing 1000 psi of force the left rear was giving 250 psi and the right rear was giving about 125 psi.

3. The difference in clamping force between the single piston GT fronts and the single piston Cobra rear is enormous. The difference is even worse than I ever dreamed. We used the even numbers to set the front pressure and then read what the back said at that point so we had some nice even data points to help quantify the info.

Here is the of the data:
Front PSI / Rear PSI
500 / 50
1000 / 250
1500 / 400
2000 / 500
2500 / 750
3000 / 850
3500 / 1000
4000 / 2200

To help with understanding the numbers and how they would feel under normal driving conditions I noted the brake pedal pressure it took to get the numbers above. Normal casual stop is about 500-1000 psi, more agressive stop is 1500-2000 psi, fronts lock at 2500-3000 psi, rears lock at the max pressure of 4000F/2200R in a panic stop.

Summary. The fronts seemed fine and gave the pressures I expected. We swapped guages several times to eliminate the possibility of a guage error. So now on to the rears. A typical FFR has 15% more tire in back and about 10% more weight in back. Now when you combine that with the fact that the rear calipers are only providing 25% of the clamping pressure as the fronts I can see why the braking is far from optimal in our cars.

Thanks again to Tim and Keith for all the help today.

Mike
 
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Mike, been thinking about braking systems and I've found a couple links that support what I believe, which is I think a braking system should NOT have near equal front to rear braking systems. I also don't think your proportioning valve is bad. As I understand what I've read, these valves aren't static adjustments. I'm not very good at explaining what I'm trying to say, so check out the links and see what you think
http://www.classicperform.com/How/How-Master-Cyl-Prop-Work.htm
http://www.chevyhiperformance.com/techarticles/71398_install_brake_proportioning_valve/index.html
http://www.familycar.com/brakes.htm

Hth
 
Tim I think we are looking at this from different perspectives. I think you are looking at the subject from the perspective of a teen driver or soccer mom. Those are the lowest common denominator that stock braking systems are built around. I am thinking this through from the perspective of a Lemans racer or Formula 1 engineer. Not that I am even close to that level, but that is the goal of my work toward a better racecar. Remember that the cars we drive are designed to be on a track not getting groceries. Please don't take offense as I run to the store in the Coupe quite often.

To prove my point here are some articles that look at this subject from my perspective. I think the difference in the approach will be obvious.

http://www.stockcarracing.com/techarticles/scrp_0412_race_car_brake_bias/index.html


http://www.circletrack.com/tipstricks/ctrp_0009_race_car_braking_force/index.html
"Correct brake bias will help you maximize the braking force available from your car, allowing you to brake later, harder, and more confidently."


http://dsr.racer.net/brake_bias.htm
"As a general rule, 60% of your braking capacity should be on the front tires. Whatever the percentage is for your particular car, the front tires should lock up slightly before the rear tires."

Note they recommend a ballpark of a 60/40 split in braking power/ bias. The data we measured the other day was a 80/20 split. This means the mustang rear brake needs to be doubled in power to even approach this rule of thumb.

http://f1-dictionary.110mb.com/brake_balance.html
"Around 10% of the retardation force is transferred from the rear axle to the front during deceleration. As speed reduces, the retardation force falls and the balance changes towards the rear. In reality, most Formula 1 cars have aerodynamic configurations that move the aerodynamic balance towards the front as the ride height reduces and the car pitches nose-down. The shift in load distribution towards the rear will be more pronounced as the speed falls."

http://books.google.com/books?id=Bj...esnum=1&ved=0CBgQ6AEwADgU#v=onepage&q&f=false
 
Yes it would Mark. Just remember it can only reduce pressure not increase. That is why I put mine in the front to reduce the front pressure down to near what the rear brakes provide. I don't think you could use it on a non-boosted system as you need all the brakes you can get when manual. I can't remember if you have manual brakes or not.

One caution... that looks just like the one I bought from Jegs which failed fairly quickly. I spoke with Jegs today and they agree it is not working correctly and will warranty it. I went with the Wilwood unit as the replacement in hopes it will be more reliable.

Failed unit: http://www.jegs.com/i/JEGS+Performance+Products/555/63020/10002/-1

New unit: http://www.jegs.com/i/Wilwood/950/260-8419/10002/-1
 
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